This paper proposes a batteryless, wireless communication circuit, which is designed to be combined with a hydrogen ion exponent (pH) sensor for the measurement of gastric acid. The proposed circuit converts the output of the biosensor into a pulse interval modulation (PIM) code and transmits the code to a base station. The circuit is powered solely by the base station via inductive coupling. Simulation results show that the circuit generates a pair of pulses in response to a shot of power supply and that the interval between the pulses, ranging from 48.μs to 132μs, depends on the pH value, ranging between 0 and 6. Each pulse is over 2V and can easily be transmitted and subsequently detected and processed by the base station. The sensor module, which consists of the proposed circuit, an ISFET as a pH sensor, and an antenna coil, could be made no larger than an ingestible capsule.